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Author Topic: Best DMX shield grounding practices  (Read 321 times)

David Allred

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Best DMX shield grounding practices
« on: May 17, 2019, 10:41:50 am »

I have a permanent exterior install.  Some runs buried in conduit which will require certain run sections to be near the 120v electrical runs that will break the "6 in rule", but we will get a much separation as we can.
The entire DMX string is about 430'.  9 fixutures, with the shortest connection of about 10 ft, the majority are about 30 ft, 2 of about 125 ft, and the controller to 1st fixture is 80 ft.  The 2) 125 ft long runs are wall and roof top runs, so separation is no problem there.  Only 25 ft of the lead run (80') would be in near proximity to electrical.

I am using Ubiquiti tough-pro with shield in PVC electrical conduit.  The DMX controller is a ADJ myDMX3 dongle in stand-alone mode. 
Where should I connect the DMX shield ground.  I have seen that it should be connected only at the control unit, but I have no ground there.  What is my next best option?  At the first light fixture in the run?   Can I simply connect to the electrical ground?

Thanks
« Last Edit: May 17, 2019, 03:08:06 pm by David Allred »
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duane massey

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Re: Best DMX shield grounding practices
« Reply #1 on: May 19, 2019, 05:07:18 pm »

I'm sure you will get some different replies, but (in my experience) ideally it should be tied to pin 1 only in the XLR. In most cases it is tied at both ends, but I have had one install where the electrical grounds were problematic so I floated the home run ground at the controller. So far I have never had an issue with DMX cables running next to electrical lines.
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Duane Massey
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Mac Kerr

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Re: Best DMX shield grounding practices
« Reply #2 on: May 19, 2019, 05:23:49 pm »

I am using Ubiquiti tough-pro with shield in PVC electrical conduit.  The DMX controller is a ADJ myDMX3 dongle in stand-alone mode. 
Where should I connect the DMX shield ground.  I have seen that it should be connected only at the control unit, but I have no ground there.  What is my next best option?  At the first light fixture in the run?   Can I simply connect to the electrical ground?

Assuming you are using Ethercon connectors it should be connected to the metal shield of the RJ45 and to the shell of the Ethercon.

Resistance to AC power induced interference is handled by the twist in the shielded pair, it has nothing to do with the actual shield which protects against RFI. The shield should still be carried through since there is plenty of opportunity for RFI in most digital systems.

Mac
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Scott Holtzman

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Re: Best DMX shield grounding practices
« Reply #3 on: May 19, 2019, 08:34:19 pm »

For long data runs fiber has become so inexpensive it makes sure that in the event of a catastrophic power issue your data cable will never be the best return path!

Sent from my VS996 using Tapatalk

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Scott AKA "Skyking" Holtzman
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David Allred

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Re: Best DMX shield grounding practices
« Reply #4 on: May 19, 2019, 10:12:37 pm »

XLR connection at the control dongle.  All other pass-through connections are in ip68 multi-port project boxes using junction blocks.  Iluminarc uses a single multi-cable dmx in and out so this was the best option for me.
Seems like my options are grounding the shield at the beginning, at the end, both, or neither.
Easy enough to try each if I have an issue.
« Last Edit: May 19, 2019, 10:16:28 pm by David Allred »
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Lyle Williams

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Re: Best DMX shield grounding practices
« Reply #5 on: May 20, 2019, 03:34:31 pm »

Rs485 is a balanced and quite high voltage digital signal.  Shielding is a luxury, not a necessity.
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David Allred

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Re: Best DMX shield grounding practices
« Reply #6 on: May 21, 2019, 09:49:55 am »

Rs485 is a balanced and quite high voltage digital signal.  Shielding is a luxury, not a necessity.

Thanks.  That is very comforting.
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